Technical Papers and Presentations

Cold season thunderstorms are a threat for wind turbines in several areas of the world because the thundercloud is much closer to the earth compared to warm season thunderstorms. As a consequence, the electric field between cloud and ground is much higher during these storms, triggering so-called upward lightning flashes. Wind turbines being tall and pointy grounded structures are particularly affected, since the electric field around the tip of the blades can be several orders of magnitude larger than the ambient electric field, sparking the initiation of frequent upward lightning strokes.

The Electrostatics physics interface (available in the AC/DC Module of the COMSOL Multiphysics^® simulation software) is used to calculate the electric field distribution at the tip of the wind turbine blades, which is input into the upward leader inception model developed by Becerra & Corray, in order to determine which wind turbines in a wind farm are most exposed to upward lightning during cold season thunderstorms. A multiparameter study, controlled via LiveLink™ for MATLAB^®

allows to evaluate the impact of the different parameters.

The model is created with the elevation profile and wind turbine location of a real wind power plant. Historical meteorological data on the thunderstorms in the area, such as the wind direction and the height of the charge in the cloud, are used as input for the model. Elevation and wind turbines are modeled as grounded 3D surface objects. The cloud is simulated as a potential surface which approaches the wind farm from a certain direction and at certain height depending on the meteorological parameters. The electric potential of the cloud is adjusted from the minimum lightning trigger voltage to the maximum expected electric potential at site. With this methodology, discharge patterns during cold season thunderstorms can be reproduced for any location in the world even before the wind power plant is constructed. This provides the opportunity to predict which of the wind turbines in a wind power plant would be most affected by upward lightning flashes. This information can be used to adapt the lightning protection in the turbine, to adjust the maintenance schedules for the wind farm or to identify the turbines which are most relevant for on-site lightning measurements.

The simulated lightning distribution is compared to measured lightning location system data and a good correlation between simulation and field data is achieved.